1. Scope of the Invention
The present invention relates to the suspension of welding apparatus from plug bodies welded in the end of tubes extended down through horizontal tube sheets. More specifically, the invention relates to linking a plug body, force fitted up into the end of a tube, with welding apparatus by a manually engageable, and disengagable, mandrel permanently mounted on the welding apparatus and insertable into the plug body.
2. Prior Art
All parts and pieces of nuclear power plants are continually inspected during fabrication and service. Elaborate inspection techniques ferret out tubes of the heat exchangers of nuclear steam generators which have failed, or are near failure. A deliberate plan is to provide a pre-determined excess of tubes for the heat exchanger. Then, if inspection decrees it prudent to remove a tube from service, sufficient tubes remain to carry on. Of course, eventually, the number of tubes plugged, removed from service, eventually force a shut down for a massive overhaul of the system. But it is practical to seal off a large number of tubes in these heat exchangers and continue their function without crippling the overall system.
The present problem assumes the inspection technique and apparatus have designated one or more tubes to be removed from service. Further, the assumption is simply that a plug body of metallic material can be jammed up into the end of the designated tube and its periphery welded to the mouth of the tube to effectively bring about their union.
Unfortunately, for this simple plan, these heat exchangers are "hot." The heat exchanger is part of the cycle containing radioactive material. Although the heat exchanger is drained of its fluids in anticipation of the tube blocking operation, a radiation level remains which must be accounted for in employing personnel for the plugging operation. The tube plugger is required to jump into the heat exchanger, locate the offending tube, and hammer a plug body into its open end, weld the body into place within a prescribed program of man-rem hours. Therefore, the less time a welder spends in the heat exchanger, the better.
Although hammering a tube body up into the end of a designated tube and welding it in place with a hand-held welding gun is not complex by objective standards, its demand for manual dexterity under the stress of the radiation threat has created problems. Plug bodies have been misaligned in hammering them into their force fit position and the guiding mandrels of welding guns have been bent and broken in forming the welds between tube and plug. The technology is demanding another step forward in the art to raise the quality of the plugging operation.